To strike Iran's nuclear facilities or not to strike? Why polls differ.

In this photo released by an official website of the Iranian supreme leader's office, Iranian supreme leader Ayatollah Ali Khamenei (l.) delivers a speech during his meeting with members of Experts Assembly in Tehran, Iran on March 8.

But if the question is put another way, and Americans are asked if they would support the US launching military action against Iran if there were evidence that Tehran is building nuclear weapons, a clear majority – 56 percent – say they would, according to a poll released Tuesday by Reuters and the Ipsos polling group.

What looks like contradictory responses is most likely explained by the differing wording: One poll asks about bombing Iran’s “nuclear program,” while the other asks specifically about military action in the event that “evidence” shows Iran is building a nuclear weapon.

But taken together, the two polls reflect to some degree the position that President Obama has staked out on Iran. As he reiterated in a Rose Garden press conference Wednesday with British Prime Minister David Cameron, the president favors a negotiated settlement for Iran’s nuclear challenge, even as he warns Iran that the time for dialogue is drawing to a close.

“The window for solving this issue diplomatically is shrinking,” Mr. Obama said, adding that the world and the US will not accept a nuclear-armed Iran. He concluded with a message to the Iranian government: “Meet your international obligations or face the consequences.”

The Reuters/Ipsos poll does suggest that Republicans are much more likely to favor striking Iran – perhaps reflecting the hawkish rhetoric on Iran from Republican presidential candidates during last week’s visit to Washington by Israeli Prime Minister Benjamin Netanyahu. While 70 percent of Republicans would support bombing an Iran that was shown to be building a nuclear weapon, 46 percent of Democrats and 51 percent of independents would support such action.

The inclusion of “evidence” in the Reuters/Ipsos poll suggests that Americans may still be operating under an “Iraq effect.” Many Americans remember that the Bush administration presented what was said to be conclusive evidence that Saddam Hussein was building and stockpiling weapons of mass destruction. The invasion revealed that those weapons did not exist.

How much “evidence” would actually be required for the public to support military action is unclear.

The results of the PIPA poll, on the other hand, suggest a different kind of Iraq effect – a broad feeling among Americans that military intervention is not a quick fix to international problems. The PIPA poll indicates that a majority of Americans believe a military strike would either only slightly delay or would in fact lead to an acceleration of Iran’s nuclear program. And nearly half believe military action would lead to a war that would last for years.

“One of the reasons Americans are so cool toward the idea of Israel attacking Iran’s nuclear program is that most believe that it is not likely to produce much benefit,” says Steven Kull, director of PIPA.

Some Iran analysts and US political leaders have started to promote the idea that it is not Iran’s nuclear program per se that is the problem, but the Iranian government. So they conclude that the US goal should be “regime change” in Iran.

But less than half of Americans – 42 percent – believe that military action would weaken the Iranian government, according to the PIPA poll. About a third believe airstrikes would actually strengthen the regime.

Mr. Kull says Americans’ reluctance toward military strikes on Iran should not be interpreted as wishful thinking that Iran has no interest in building a bomb. On the contrary, he says, most Americans are pessimistic about Iran’s intentions.

The poll found that 58 percent believe Iran has already decided it wants the bomb and is actively working to build it.